DueDateCalculatorduedate-calculator.com

How to Calculate Your Due Date

There are four main methods doctors use to estimate your due date. Learn which one applies to you and how to calculate it.

Ashok Kumar Poudel
Written by
Ashok Kumar Poudel
Health & Wellness Writer
Dr. Bina Basnet
Medically reviewed by
MBBS, MD — Gynecologist & Obstetrician
Last reviewed:
Feb 2026

Method 1: Last Menstrual Period (LMP)

The LMP method is the most widely used approach. Take the first day of your last menstrual period and add 280 days (40 weeks). This is known as Naegele’s Rule, developed in the 19th century and still the global standard.

EDD = LMP + 280 days
Or: LMP + 1 year − 3 months + 7 days
Adjustment: ± (your cycle length − 28) days

Best for: Anyone with a known LMP and regular cycles.
Accuracy: ±2 weeks without ultrasound confirmation.

Use LMP Calculator →

Method 2: Conception Date

If you know when you conceived, add 266 days (38 weeks). This counts from actual fertilization rather than your last period. Conception typically occurs 14 days after LMP in a 28-day cycle.

EDD = Conception Date + 266 days

Best for: Those who tracked ovulation, used ovulation tests, or know exactly when they conceived.
Accuracy: ±7 days if conception date is known precisely.

Use Conception Calculator →

Method 3: Ultrasound Dating

An ultrasound measures the size of your baby to estimate gestational age. Crown-Rump Length (CRL) measurement in the first trimester (up to 14 weeks) is the most accurate dating method — typically within ±5 days. After 20 weeks, accuracy decreases to ±2–3 weeks.

EDD = Scan Date + (280 − Gestational Age at Scan)
GA at scan = weeks × 7 + days

Best for: Confirming or correcting LMP-based dates; irregular cycles; uncertain LMP.
Accuracy: ±5 days (first trimester CRL); ±2–3 weeks (second trimester).

Use Ultrasound Calculator →

Method 4: IVF Transfer Date

For IVF pregnancies, the due date is calculated from the embryo transfer date. Since the embryo age is known precisely (Day 3, Day 5, or Day 6), the calculation is highly accurate.

Day 5 transfer: EDD = Transfer Date + 261 days
Day 3 transfer: EDD = Transfer Date + 263 days
Day 6 transfer: EDD = Transfer Date + 260 days

Best for: IVF, FET, and other assisted reproductive technology pregnancies.
Accuracy: ±1–3 days (most precise method available).

Use IVF Calculator →

Frequently Asked Questions

Common questions answered by our medical team

A first-trimester ultrasound (8–14 weeks) using Crown-Rump Length (CRL) measurement is considered the most accurate method — typically accurate to within ±5 days. LMP is the most commonly used starting method, confirmed by early ultrasound.
Calculate Your Due Date Now →